Leionema praetermissum, is a shrub with warty stems covered in hairs, white flowers with spreading petals, and prominent stamens.

The leaves are smooth, narrow, linear to lance shaped, 20–35 mm (0.79–1.38 in) long, edges slightly rolled under, arranged alternately, sometimes crowded, smooth and sessile or on a short petiole 2 mm (0.079 in) long, and ending with a sharp point.

[2][3][4] Leionema praetermissum was first formally described by Phillipa Alvarez and Marco Duretto in 2019 and the description was published in the journal Telopea.

[3][5] The specific epithet (praetermissum) is in reference to "this species having been identified as an undescribed taxon for at least three decades before being formally described".

[1] This species has a restricted distribution, it grows in wetlands adjacent to water courses in sand, amongst boulders in vegetation thickets along the Colo River in the Wollemi National Park in New South Wales.